T&C general application failure mode and potential cause analysis of the wiring harness system series (1)
2021-05-12 12:04 admin
Some friends asked the author to share the analysis of failures and failures because our wiring harness engineers spend a considerable part of their energy on repairing cars in their daily work.
Next, the author will use a few pages to summarize the common problems and potential causes of T&C (terminal and connector) in the application (this sub-series focuses on analyzing the issues of the application), here is not all possible causes Listed out, write out the more typical, welcome everyone to leave a message and discuss.
1. The pairing force of the male and female connectors is too large
Common failure modes:
1. Difficulty in assembly;
2. The terminal is ejected.
This problem is still a widespread problem on wiring harnesses. Generally speaking, it is the feedback from the OEM. Of course, there are also false alarms. Because the connectors have different power distributions, they are always labor-saving. When it reaches a strong one, it will make the assembler loud. They have to pretend to be so much a day and have the same reaction.
This seems to be a contradiction in the standard design because the terminal must maintain good contact and connectivity. The positive pressure of the connection of the female terminal on the male terminal should not be too small, and the male terminal is inserted into the female terminal:
F=μ×Fn
As the positive pressure increases, the insertion force also increases.
When the connector has a large number of holes and a large number of terminals, you will find that the insertion force will be huge. Of course, this is a normal phenomenon. But too large (see UScar-25) is the problem.
In general, the underlying causes are as follows:
1. Incorrect terminal selection (non-designated model terminal)
This is not too common, but we have also discovered it (this requires a product engineer to take two steps, and the matching is not careful).
2. The terminal is inserted in the wrong direction
Some connectors are designed without error prevention. The terminals can be inserted in both directions, but only one path is correct. After the order is reversed, it will result in failure to match or excessive force. This phenomenon usually occurs in the male terminal.
3. The header size of the self-opening mold on the equipment side is out of tolerance
This is a widespread phenomenon. Like a wire harness, how high-end can this connector terminal be in the eyes of many people? Find two college students and copy them. But this is not the case. T&C is a technical professional. You can copy its size, but you can't know its morainal size, how big its tolerance is, and how many vital dimensions it has. In some large manufacturers, there are even dozens of key dimensions on drawing a connector (note the key dimensions). However, it is a common phenomenon to open molds to manufacture on the equipment side when the technical reserves are not enough, so the reason for this is very prominent.
4. Reworked terminals
The terminal is inserted into the wrong hole. It is widespread to exit and re-insert. Most connectors also allow this operation. However, this step must be controlled in the wire harness factory. Ordinary operators should prohibit rework operations, but the actual situation But isn't easy to maintain. To pursue the so-called efficiency and rhythm, sometimes this is not the case. Once a sizeable foreign-funded company found such a situation, their quality department slapped their chests. We would never allow ordinary operators to adjust the terminals, but the facts soon got beaten. Operators who have not been trained can damage the terminals due to irregular operations while retracting the terminals, causing a series of situations such as twisting and skewing. This can lead to a significant deviation in the terminal position after reinsertion, which will cause problems when the male and female connectors are matched.
5. The terminal crimping is unqualified, and the terminal is bent or twisted
Since each wire harness factory's quality of the crimping die is different, the terminal deformation after crimping is another. Generally speaking, during the terminal crimping process, due to the flow of the base material under the crimping force, the final terminal There will always be a certain degree of deformation and distortion. Still, the amount of deformation needs to be controlled. This point needs to be considered when making the crimping die. The following parameters are for reference:
6. The terminal is stressed by the wiring harness (the winding tape position is not appropriate)
There are many discussions on this issue, but there are also many misunderstandings. Generally speaking, it is unnecessary to be too constrained on the amount of non-binding distance reserved for tape wrapping. The most fundamental principle is: let the terminal not be affected or as little as possible Subject to the pulling stress of the wire, especially the airports on both sides of the connector.
We all know that the terminal has a shaking amount in the connector hole. This shaking amount is designed to allow the male and female terminals to have a certain amount of necessary adaptive adjustment freedom when they are mated.
If the tape is wrapped too close to the connector, it will cause the wires on both sides to be taut, which will cause the terminals to lose free movement and become skewed. Then there may be problems during mating. Of course, there will be other problems in use, and we will continue to discuss them in the follow-up.
The following picture is a very typical case of excessive winding:
Remind everyone to pay attention: this point must not be taken. Unreasonable bandaging will cause a series of serious problems, which will be explained in subsequent chapters.
As mentioned at the beginning, other reasons can also cause the problem of large distribution of male and female connectors, such as manufactured connectors, shrinkage, deformation, burrs, and so on.
Please continue to follow me, and I will publish the following article.
Next, the author will use a few pages to summarize the common problems and potential causes of T&C (terminal and connector) in the application (this sub-series focuses on analyzing the issues of the application), here is not all possible causes Listed out, write out the more typical, welcome everyone to leave a message and discuss.
1. The pairing force of the male and female connectors is too large
Common failure modes:
1. Difficulty in assembly;
2. The terminal is ejected.
This problem is still a widespread problem on wiring harnesses. Generally speaking, it is the feedback from the OEM. Of course, there are also false alarms. Because the connectors have different power distributions, they are always labor-saving. When it reaches a strong one, it will make the assembler loud. They have to pretend to be so much a day and have the same reaction.
This seems to be a contradiction in the standard design because the terminal must maintain good contact and connectivity. The positive pressure of the connection of the female terminal on the male terminal should not be too small, and the male terminal is inserted into the female terminal:
F=μ×Fn
As the positive pressure increases, the insertion force also increases.
When the connector has a large number of holes and a large number of terminals, you will find that the insertion force will be huge. Of course, this is a normal phenomenon. But too large (see UScar-25) is the problem.
In general, the underlying causes are as follows:
1. Incorrect terminal selection (non-designated model terminal)
This is not too common, but we have also discovered it (this requires a product engineer to take two steps, and the matching is not careful).
2. The terminal is inserted in the wrong direction
Some connectors are designed without error prevention. The terminals can be inserted in both directions, but only one path is correct. After the order is reversed, it will result in failure to match or excessive force. This phenomenon usually occurs in the male terminal.
3. The header size of the self-opening mold on the equipment side is out of tolerance
This is a widespread phenomenon. Like a wire harness, how high-end can this connector terminal be in the eyes of many people? Find two college students and copy them. But this is not the case. T&C is a technical professional. You can copy its size, but you can't know its morainal size, how big its tolerance is, and how many vital dimensions it has. In some large manufacturers, there are even dozens of key dimensions on drawing a connector (note the key dimensions). However, it is a common phenomenon to open molds to manufacture on the equipment side when the technical reserves are not enough, so the reason for this is very prominent.
4. Reworked terminals
The terminal is inserted into the wrong hole. It is widespread to exit and re-insert. Most connectors also allow this operation. However, this step must be controlled in the wire harness factory. Ordinary operators should prohibit rework operations, but the actual situation But isn't easy to maintain. To pursue the so-called efficiency and rhythm, sometimes this is not the case. Once a sizeable foreign-funded company found such a situation, their quality department slapped their chests. We would never allow ordinary operators to adjust the terminals, but the facts soon got beaten. Operators who have not been trained can damage the terminals due to irregular operations while retracting the terminals, causing a series of situations such as twisting and skewing. This can lead to a significant deviation in the terminal position after reinsertion, which will cause problems when the male and female connectors are matched.
5. The terminal crimping is unqualified, and the terminal is bent or twisted
Since each wire harness factory's quality of the crimping die is different, the terminal deformation after crimping is another. Generally speaking, during the terminal crimping process, due to the flow of the base material under the crimping force, the final terminal There will always be a certain degree of deformation and distortion. Still, the amount of deformation needs to be controlled. This point needs to be considered when making the crimping die. The following parameters are for reference:
6. The terminal is stressed by the wiring harness (the winding tape position is not appropriate)
There are many discussions on this issue, but there are also many misunderstandings. Generally speaking, it is unnecessary to be too constrained on the amount of non-binding distance reserved for tape wrapping. The most fundamental principle is: let the terminal not be affected or as little as possible Subject to the pulling stress of the wire, especially the airports on both sides of the connector.
We all know that the terminal has a shaking amount in the connector hole. This shaking amount is designed to allow the male and female terminals to have a certain amount of necessary adaptive adjustment freedom when they are mated.
If the tape is wrapped too close to the connector, it will cause the wires on both sides to be taut, which will cause the terminals to lose free movement and become skewed. Then there may be problems during mating. Of course, there will be other problems in use, and we will continue to discuss them in the follow-up.
The following picture is a very typical case of excessive winding:
Remind everyone to pay attention: this point must not be taken. Unreasonable bandaging will cause a series of serious problems, which will be explained in subsequent chapters.
As mentioned at the beginning, other reasons can also cause the problem of large distribution of male and female connectors, such as manufactured connectors, shrinkage, deformation, burrs, and so on.
Please continue to follow me, and I will publish the following article.